Sleep, EEG and mental function variables were studied in 44 subjects diagnosed as having probable senile dementia of the Alzheimer's type (SDAT) and 22 controls matched for age and minimal depression. Results indicate that sleep, EEG and mental function variables all undergo significant change even in the early, mild stage of SDAT, with further change in the moderate and severe stages of dementia. Mental function variables also underwent significant decline across levels of dementia. Sleep and mental function variables had strong power in correctly classifying subjects into control vs. mild dementia groups (90 and 100%, respectively). Dominant occipital rhythm frequency, a clinical EEG measure, also discriminate as well (75%). The results indicate that sleep and EEG variables discriminate well for early, mild SDAT in minimally depressed aged individuals.